This invention relates, in general, to radar systems and, more specifically, to apparatus and methods for processing radar signals to determine the direction to the source of the signal energy.
With phased array antenna systems having many separate antenna elements or output ports, a large amount of signal information can be acquired for processing by various methods. Generally, the phase and amplitude of each separate antenna element or output port at different instants of time are used by the prior art processing techniques for obtaining the desired information. The desired information may be the presence of and direction toward two or more signal sources located within the normal bandwidth of the main lobe of radiation of the antenna. These sources may be targets or jammers, or a combination of the two. Discriminating between the sources in regions within the beamwidth of the antenna is known as "super resolution" and requires sophisticated signal processing to see signal sources located so close together. Basically, the process determines the angle or direction from the receiving antenna to the signal sources.
Several processing methods have been used for giving super resolution capabilities to radar signal processors. These methods include the maximum entropy method (MEM), the maximum likelihood method (MLM), and the thermal noise method (TNM). In each case, there is the requirement that matrices formed from the antenna output signal components, including the in-phase (I) and quadrature (Q) components, be mathematically manipulated to produce the signal source direction. Since the size of such matrices is proportional to the number of antenna elements or output ports employed, the number of values which must be mathematically manipulated becomes very large and the processing speed of the processor is required to be high in order to achieve the results in the desired time periods. Consequently, it is desirable, and it is an object of this invention, to provide apparatus and methods for determining the location of signal sources without having to perform all of the mathematical steps on the signal matrices.